As high resolution and large screen in a PDP are realized, a 65-inch television receiver or a large-sized public display device is being manufactured and a product larger than 100 inch is also planned. Particularly in the case of a PDP dedicated for a television receiver, application to full spec Hi-Vision, in which the number of scan lines is twice or more than that in the known NTSC system, is under progress.
Basically, a PDP is configured to include a front plate and a rear plate. The front panel is configured to include a glass substrate made of sodium borosilicate based glass using a float method, display electrodes including strip-shaped transparent electrodes and bus electrodes formed on a main surface of the glass substrate, a dielectric layer that covers the display electrodes and serves as a capacitor, and a protective layer that is formed on the dielectric layer and made of magnesium oxide (MgO). On the other hand, the rear plate is configured to include a glass substrate provided with a fine hole for ventilation and discharge gas filling, strip-shaped address electrodes formed on a main surface of the glass substrate, a base dielectric layer that covers the address electrodes, barrier ribs formed on the base dielectric layer, and a phosphor layer that is formed between the barrier ribs to emit light in red, green, and blue colors.
In addition, peripheries of the front plate and the rear plate are airtight sealed by sealant in a state in which surfaces, on which electrodes are formed, of the front plate and the rear plate are disposed opposite to each other. In addition, an exhaust pipe for ventilation and discharge gas filling is sealed on the rear plate with a sealing tablet and ventilation of a discharge space, which is divided into barrier ribs by the exhaust pipe, and filling of discharge gas (in the case of Ne—Xe, pressure of 53200 Pa to 79800 Pa) are performed. Here, the exhaust pipe is fused and sealed by locally heating and melting (chipping off) a proper place thereof.
As sealant used for sealing of the dielectric layer, peripheries of the front and rear plates, and the exhaust pipe, low-melting-point glass (also referred to as a ‘frit glass’) having lead oxide as a main component has been generally used. The frit glass includes amorphous frit glass that has an amorphous characteristic without being crystallized even if the glass is heated and crystallized frit glass that is crystallized by heating. In many cases, one of the two types of glass is selected in consideration of matching with a process of manufacturing a PDP.
Moreover, in consideration of an environmental issue in recent years, it is requested that a non-lead based material called ‘lead free’ or ‘leadless’ and not containing a lead component be used even for a PDP. Examples of bismuth oxide based sealant and phosphate based (for example, phosphate-tin oxide based) sealant not containing a lead component are disclosed (for example, refer to Patent Documents 1 and 2).
However, in the case of sealant having phosphate-tin oxide based low-melting-point glass as a main component that has been proposed as non-lead sealant, a resistance to water is weak as compared with lead oxide based sealant that has been used in the related art. Accordingly, there is a problem in that it is difficult to sufficiently maintain the airtight state of a PDP. For this reason, bismuth oxide based sealant has been drawing attention as a non-lead material. In addition, in the case of the non-lead sealant having a bismuth oxide based frit glass as a main component, a softening point tends to be high after temporary baking, which is not seen in the known amorphous frit containing lead. Moreover, the leadless sealant having the bismuth oxide based frit glass as a main component is crystallized as the baking temperature increases.
In the relate art, the exhaust pipe has been formed of borosilicate based glass containing lead since a softening point temperature is relatively low and workability in a sealing process is excellent. However, due to an environmental issue, a trend is changing in the direction in which borosilicate based glass not containing lead is used.
FIG. 7 is a cross-sectional view illustrating the periphery of an exhaust pipe in a known PDP in which sealant or the exhaust pipe is formed of non-lead glass. As shown in FIG. 7, in PDP 50, front plate 52 and rear plate 53 are airtight sealed by sealant 54. Further, exhaust pipe 51 is airtight sealed by sealing tablet 55 having hole 33.
However, although leadless materials are used for rear plate 53, exhaust pipe 51, and sealing tablet 55, the non-lead materials have different physical characteristics. Among the physical characteristics, particularly in the case when coefficients of thermal expansion are different, ring-shaped distortion resulting from a stress occurs in sealed part 56 in which exhaust pipe 51 is sealed on rear plate 53. Accordingly, a problem occurs in that crack damage occurs or the airtight state deteriorates to cause leak failure.
In the case of non-lead sealant having bismuth oxide based frit glass as a main component, a softening point tends to be high after temporary baking. For this reason, it is necessary to set the temperature in sealing processing high. As the temperature in sealing processing increases, distortion resulting from a stress occurs noticeably, which also increases a failure frequency in a manufacturing process.
Moreover, even though it is easy to match characteristics, such as coefficients of thermal expansion of exhaust pipe 51 and the glass substrate used for rear plate 53 with each other, it is difficult to match a material for forming rear plate 53 or exhaust pipe 51 and characteristics, such as a coefficient of thermal expansion because the frit glass used for sealing tablet 55 is a low-melting-point glass.
Therefore, it is necessary to select frit glass and detect matching, and many tests are required to secure a processing condition for preventing damage or leak failure of a sealed part from occurring due to a difference of characteristics, such as coefficients of thermal expansion, by controlling the temperature, time, a heating rate, a cooling rate, and the like in consideration of characteristics.    [Patent Document 1] Japanese Patent Unexamined Publication No. 2004-182584    [Patent Document 2] Japanese Patent Unexamined Publication No. 2003-095697